In a reaction for producing propylene oxide from hydrogen, oxygen and propylene by using palladium and TS-1 as catalysts, it has been reported that the amount of propylene oxide formed is increased and the amount of the by-product propane is reduced, when using water and methanol as solvents and adding ammonium hydroxide (see Patent Document 1, for example). Further, a method of a reaction for producing propylene oxide from hydrogen, oxygen, and propylene by using palladium and TS-1 as catalysts has been reported, wherein water and methanol are used as solvents and an ammonium hydrogencarbonate salt is added (Patent Document 2), or cesium phosphate is added to an aqueous solvent (Patent Document 3). In Patent Document 2 (paragraph [0008]) and Patent Document 3 (paragraph [00091]), there are such descriptions that titanium silicalite which is titanium zeolite having relatively small pores is preferable for oxidation of propylene, and that use of TS-1 titanium silicalite is absolutely advantageous. However, these methods are not necessarily satisfactory from the viewpoint of reaction efficiency.
Furthermore, a method for producing propylene oxide from hydrogen, oxygen and propylene has been reported, wherein Pd and a Ti-MWW catalyst or a catalyst containing a layered titanosilicate that is a precursor of Ti-MWW, each of which has pores of a 12-membered oxygen ring is used in an acetonitrile solvent (see non-Patent Document 1, for example). However, the efficiency is not necessarily satisfactory, either.    Patent Document 1: JP 2002-511455 A    Patent Document 2: JP 2005-514364 A    Patent Document 3: JP 2005-508362 A    Non-Patent Document 1: Next Generation Chemical Process Technological Development in 2002; Non-Halogen Chemical Process Technological Development Achievement Report; 152-180 (2003)